Metropolitan Transportation Authority (MTA) Electrical Practice Test

A saturable reactor is used in a magnetic amplifier to control or amplify a circuit. The core’s magnetic permeability changes with the level of bias current, so the inductance seen by the signal on the main winding can be driven up or down by the DC control winding. By biasing the core toward saturation, the inductance drops and the AC signal can pass more readily, effectively regulating or amplifying the output based on the control current. This is the defining function of a magnetic amplifier. The other terms aren’t devices that perform this kind of regulation: inductance is a property of a coil, line of force refers to magnetic flux lines, and load is simply what the circuit powers rather than a regulating element.